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• Removing Silence from m4a files using ffmpeg

  27 juin 2015, par Tejas Shah

  I have an audio file which has both leading and trailing silence and with the following specifics :

  Codec : MPEG AAC Audio (mp4a) Channels : Stereo Sample rate : 44100 Hz Bitrate : 253 kbps

  I want to remove the silences AND keep the quality intact.

  So far I’ve tried

  ffmpeg -i 1.m4a -af silenceremove=1:0.5:0:1:0.5:0 2.m4a 

  This is supposed to remove both the leading and trailing silences.
  But for some reason it doesn’t remove the trailing silence. This seems to be a recurring problem. Found the following on another forum.

  http://ffmpeg-users.933282.n4.nabble.com/How-to-delete-digital-silence-tp4667256p4667356.html

  Also, ffmpeg reduces the bitrate to 128kbps. This I could fix by adding -ab 253k and making the command :

  ffmpeg -i 1.m4a -af silenceremove=1:0.5:0:1:0.5:0 -ab 253k 3.m4a 

  Now the problem is that the trailing silence isn’t removed and when I want to process a batch of files I can’t use the same bitrate (like 253kbps ) for every file. I’d like to know how VBR could be used for this case.

  I know I can use sox and use the silence and reverse features to trim the silences.

  http://digitalcardboard.com/blog/2009/08/25/the-sox-of-silence "Example 3 in this post"

  But sox has the following problems :

  1. It can’t handle m4a files, I had to convert all files to mp3.

  2. When using the silence filter in sox it caps the bitrate at 128kbps.

     sox 1.mp3 2.mp3 silence 1 0.5 1% reverse silence 1 0.5 1% reverse

• lavf : Replace the ASF demuxer

  15 juin 2015, par Alexandra Hájková

  lavf : Replace the ASF demuxer
  The old one is the result of the reverse engineering and guesswork.
  
  The new one has been written following the now-available specification.
  This work is part of Outreach Program for Women Summer 2014 activities
  
  for the Libav project.
  The fate references had to be changed because the old demuxer truncates
  
  the last frame in some cases, the new one handles it properly.
  
  The seek-test reference is changed because seeking works differently
  
  in the new demuxer. When seeking, the packet is not read from the stream
  
  directly, but it is rather constructed by the demuxer. That is why
  
  position is -1 now in the reference.
  Signed-off-by : Anton Khirnov <anton@khirnov.net>
  

  • [DBH] Changelog
  • [DBH] libavformat/asf.h
  • [DBH] libavformat/asfdec.c
  • [DBH] libavformat/asfenc.c
  • [DBH] libavformat/version.h
  • [DBH] tests/ref/fate/wmv8-drm-nodec
  • [DBH] tests/ref/seek/lavf-asf

• lavf : Replace the ASF demuxer

  15 juin 2015, par Alexandra Hájková

  lavf : Replace the ASF demuxer
  The old one is the result of the reverse engineering and guesswork.
  
  The new one has been written following the now-available specification.
  This work is part of Outreach Program for Women Summer 2014 activities
  
  for the Libav project.
  The fate references had to be changed because the old demuxer truncates
  
  the last frame in some cases, the new one handles it properly.
  
  The seek-test reference is changed because seeking works differently
  
  in the new demuxer. When seeking, the packet is not read from the stream
  
  directly, but it is rather constructed by the demuxer. That is why
  
  position is -1 now in the reference.
  Signed-off-by : Anton Khirnov <anton@khirnov.net>
  

  • [DH] Changelog
  • [DH] libavformat/asf.h
  • [DH] libavformat/asfdec.c
  • [DH] libavformat/asfenc.c
  • [DH] libavformat/version.h
  • [DH] tests/ref/fate/wmv8-drm-nodec
  • [DH] tests/ref/seek/lavf-asf